The present invention relates to vibration and/or shock absorbing devices, and more particularly, to an elastomer and fluid-filled device for isolating and damping vibration and shock between translating structures. The present invention also relates to compensator elements advantageous for use in vibration and/or shock absorbing devices.
Devices utilizing elastomers and fluid-filled chambers have been used for isolating and damping vibration and shock. These devices are typically used in the transportation industry, such as in mounts for aircraft and automobile engines.
The combination of elastomer elements and fluid-filled chambers is desirable for improving the overall isolating and damping characteristics of the device. The elastomer element is mainly responsible for bearing the load, but also provides some damping. Conversely, although offering little load bearing support, fluid-filled chambers can be designed to dramatically improve the isolation and damping characteristics of the device. These devices are often designed to perform best at specific xe2x80x9ctunedxe2x80x9d or xe2x80x9cnotchxe2x80x9d frequencies. Most of these devices require volume compensators to accommodate variations in the pressure of the fluid caused by temperature and/or volume changes.
An example of such a device is a fluid-filled mount, which generally includes a pair of opposed variable volume fluid-filled chambers separated by an elongate passageway or track. Within the track is a mass or slug of fluid that may be designed to vibrate out of phase with the vibrations of the system, thus canceling or reducing the transmitted vibration. Thus, the track provides a fluid mass of a desired configuration that enables the mount to be designed, or tuned, to provide desirable dynamic operating characteristics.
There are two types of mounts: a single-action type and a double-action type. A single-action mount has one chamber with a substantially higher volume stiffness than the other. Changes in the volume of the higher stiffness chamber, such as by changes in ambient temperature, are relieved by changes in the volume of the lower stiffness chamber. On the other hand, double-action mounts have two high volume stiffness chambers. While double-action mounts may provide desirable dynamic operating characteristics over single-action mounts, such as increased volume stiffness, changes in the ambient temperature adversely affect their performance. A dynamically isolated, low volume stiffness chamber, typically referred to as a volume compensator chamber, may be connected to double-action mounts to enhance their performance. One such example is found in U.S. Pat. No. 4,811,919 to Jones, issued to the assignee of the present application.
In an attempt to insure that the designed performance is achieved, many prior art devices incorporate mechanisms to account for variations in the volume and pressurization of the fluid. Typically, these devices incorporate an elastic compensator element adjacent to the fluid-filled chamber to compensate for changes in the fluid volume in order to maintain a designed fluid pressure. The elastic compensator element may form a wall of the fluid-filled chamber, or the compensator element may comprise an additional chamber separate from, but interconnected with, the fluid-filled chamber. Examples are found in U.S. Pat. No. 5,413,320 to Herbst and WO 97/30895 to McGuire.
A potential problem with the use of a compensator element, however, is that the elasticity and spring rate of the compensator element is often not sufficient to insure proper pressurization of the fluid. In these cases, additional mechanisms are required. Prior art devices have utilized gas pressurized chambers and/or mechanical springs cooperating with the compensator element and fluid-filled chamber. These mechanisms supply the compensator element with additional resistance to deformation and thereby insure the designed fluid pressure within the fluid-filled chamber. These solutions, however, may be disadvantageous by adding additional parts, cost, space and weight to the device.
For example, gas pressurized or air-tight chambers generally require precisely machined parts and additional sealing elements to maintain their pressurization. Because of the difficulty in sealing these chambers, it is not uncommon for them to lose some of their pressurization. A change of pressurization in these chambers, however, can result in loss of performance under certain conditions. Further, many pressurized chambers require expensive valves to supply and maintain the chamber pressure. Additionally, the spring rate caused by a pressurized chamber generally increases with increased pressure in the device, which can lead to performance degradation as the pressure of the fluid exceeds the designed pressure. Thus, there are numerous disadvantages to utilizing pressurized chambers cooperating with an elastomer compensator element.
Similarly, the use of mechanical springs may be disadvantageous. Springs, usually in combination with a metal plate or piston adjacent to the compensator element, add additional parts, complexity and weight to a device. Further, the use of springs may require additional space for compression and expansion, and thus add additional bulk to the device. Springs also may disadvantageously affect performance because of their increasing spring rate up to their compressive limit. As with pressurized chambers, this increased spring rate may cause the fluid in the device to exceed the designed pressure and thereby adversely affect the performance of the device. Therefore, mechanical (helical or conical coil) springs, like air pressurized chambers, may disadvantageously increase the cost, complexity, maintainability and weight of isolation and damping devices.
Further, in certain prior art devices, plates form a wall of a fluid-filled chamber. In combination with bolts and o-rings, for example, the plate seals in the fluid. All of these components add cost to the device, both in material and in assembly time. Additionally, difficulties often arise in completely filling and satisfactorily sealing a chamber full of fluid, as the placement and tightening of the plate tend to cause the fluid to overflow and get between the plate and the o-ring, causing a bad seal. Also, improper sealing or defects in the o-ring can lead to a loss of fluid, and thus a degradation or loss of performance of the device. Thus, a solution to these problems is desired to reduce the cost and improve the performance of isolation and damping devices.
The present invention overcomes the above-noted disadvantages of prior art isolators and dampers. In a first aspect, the present invention comprises a compensator element, for use in a vibration control device having a housing and at least one fluid-filled chamber, comprising an elastic layer in fluid communication with the fluid-filled chamber and disposed in sealing engagement with a portion of the device, and a deformable elastomer stiffener cooperative with the elastic layer for providing static pressurization to the at least one fluid-filled chamber. The stiffener is preferably integral with the elastic layer, thereby comprising a one-piece compensator element that is economically manufactured, such as by molding. In one preferred embodiment, the stiffener comprises a cylindrical column. The configuration of the compensator element and stiffener may vary by application and desired performance, however, and may comprise other shapes. For example, the compensator element may be oval or square and the stiffener may comprise one column or a plurality of columns. The plurality of columns may be co-axial cylindrical columns. Also, other stiffener configurations, such as square columns, oval columns, a plurality of dividing walls, etc. may be utilized. Further, the compensator element may comprise a seal bead along the perimeter of the deformable structure. The bead forms a seal to contain a fluid in the fluid-filled chamber.
Additionally, compensator element beneficially may provide a reduced rate of change in volume stiffness between a point of initial deformation and a point of maximum deformation. Similarly, the stiffener may have a reduced rate of change in spring rate that corresponds to the reduced rate of change in volume stiffness of the compensator element. The reduced rate of change in volume stiffness is a result of the volume stiffness decreasing at a point corresponding to the substantial collapse of the stiffener member.
In another aspect, the present invention comprises a device for controlling vibration and/or shock between two structures, comprising a housing for fastening to a first structure, a variable volume fluid chamber, and a support for attaching to a second structure. Translation between the housing and the support changes the fluid pressure within the chamber. Further, the present invention provides a deformable compensator element having an elastic layer in fluid communication with the fluid-filled chamber and disposed in sealing engagement with a portion of the device, and a deformable elastomer stiffener cooperative with the elastic layer for providing static pressurization to the fluid chamber. The compensator element may further comprise a seal bend along the perimeter of the elastic layer. The bead forms a seal to contain fluid in the fluid chamber. Additionally, the fluid chamber may be sealed at the housing with a bond formed utilizing an adhesive, such as acrylic or epoxy.
The compensator element may further have a reduced rate of change in volume stiffness between a point of initial deformation and a point of maximum deformation. The rate of change in volume stiffness decreases at a point corresponding to the substantial collapse of the stiffener. Similarly, the stiffener preferably has a reduced rate of change in spring rate that corresponds to the reduced rate of change in volume stiffness of the compensator element.
In a further aspect, a double-action fluid mount comprises a primary fluid system, a volume compensator and a deformable compensator element. The primary fluid system is defined by a first variable volume fluid chamber fluidly interconnected to a second variable volume fluid chamber. The volume compensator has an auxiliary chamber fluidly connected to, but dynamically isolated from, the primary fluid system. The compensator element comprises ail elastic layer in fluid communication with the auxiliary chamber and disposed in sealing engagement with the volume compensator, and a deformable elastomer stiffener cooperative with the elastic layer for providing static pressurization to the primary fluid system. Preferably, the stiffener member is integrally formed with the compensator element. The stiffener may form a cylindrical column or a plurality of columns. The stiffener preferably has a reduced rate of change in spring rate that corresponds to a reduced rate of change in volume stiffness of the compensator element. The reduced rate of change in volume stiffness is a result of the volume stiffness decreasing at a point corresponding to the substantial collapse of the stiffener member.
The mount may also comprise a housing for attachment to a first structure. Within the housing is an elastomer member that at least partially forms the first variable volume chamber and the second variable volume chamber. A support, connected to a piston that divides the first chamber and the second chamber, may be provided for attachment to a second structure. Additionally, a seal bead formed at the perimeter of the compensator element seals one end of the auxiliary chamber. Also, the invention may comprise an adhesive bond between the housing and the elastomer member to seal one end of one of the variable volume fluid chambers.
In one feature, the present invention advantageously comprises a volume compensator having an integral stiffener that provides additional volume stiffness.
In another feature the present invention provides a volume compensator having a reduced number of parts, which increases the reliability of the device.
An advantage of the present invention is its reduced cost and increased maintainability.
A further feature of the present invention is to provide an efficient compensator that maximizes the compensator volume for a given space by eliminating parts.
Another advantage of the device is the adhesive bond that seals, at least at one end, a variable volume fluid chamber, thereby eliminating mechanical parts and increasing reliability.
Further features and advantages of the present fluid-filled vibration and/or shock absorbing devices and compensator elements for use therein are provided by the drawing figures and the following more detailed description.